1. Field of the Invention
This invention relates to a flame retarding prepolymer composition, and to its method of preparation and application. A tetrakis(hydroxymethyl)phosphonium salt is the main ingredient.
2. Description of the Prior Art.
Currently investigative efforts dealing with the matter of conservation of energy and that of the minimizing pollution in all fields indicate that both the textile industry and the United States Department of Agriculture have likewise been concerned. Flame retardant finishes for cotton, for textiles, and for all other flammable materials have been investigated substantially. The cotton textile literature indicates that flame retardant finishes must be very carefully evaluated before the finished product reaches the consumer because of their potential hazards to humans, to plants and to animals, directly or indirectly.
Textile finishes available for meeting current government flammability regulations for cotton are generally based on only three flame retarding compounds. These chemicals are the condensate of bis(betachloroethyl)vinyl phosphonate and alkyl phosphonate, N-methylol dimethyl phosphonopropionamide, and tetrakis(hydroxymethyl)phosphonium salts, generally known as THP salts. Children's sleepwear cotton flannelette has been in the past finished with the THP salt or a condensation product by an ammonia gas cure. The ammonia gas cure has been preferred because the finished fabric generally has had relatively high strength and a soft hand. There have been problems with this process, among which is the release of unpleasant and irritating gases and the design of the gaseous reactor for production scale operations.
U.S. Pat. No. 3,607,356, in the prior art, discloses steps for imparting flame retardance to cellulosic fabric by the process of applying the THP salt to the substrate and then employing ammonia gas to cause its polymerization in the substrate. Among the problems encountered here is the lack of a uniform application on fabrics, ammoniation reactor design difficulties, pollution resulting from the release of gases from the reactor, such as ammonia and formaldehyde, which are irritating and toxic. Apart from textiles it has been determined that THP salts combined with an ammonia gas cure have not been adaptable to substrates such as structural members generally employed in construction of buildings.
U.S. Pat. No. 3,310,420 deals with numerous variations of flame retardant treatments; however the section which closely relates to the instant invention uses ammonia cure, as does the cited U.S. Pat. No. 3,607,356, and is encumbered by the same problems.
U.S. Pat. No. 3,846,155 deals with the apparatus of the ammonia cure process of the cited U.S. Pat. No. 3,607,356. Obviously the same problems are present.
U.S. Pat. No. 3,784,356 deals with the same concept of the THP and ammonia cure but the known process is improved by providing a liquid cure instead of a gaseous ammonia cure, thus removing the need for an ammonia reactor. The liquid ammonia cure employs anhydrous ammonia and urea. The initial step of applying the THP still required heat drying and does not at this stage contain all of the ingredients of phosphorus, methyl, and amine groups to form the flame retardant polymer, i.e., it is not a prepolymer.